Optical Pickup Control Circuit

ABSTRACT

In an optical disc playback device, focus and tracking balance amounts are automatically adjusted to specified amounts. An error rate from an error correction circuit for performing error correction of data played back from an optical disk using the optical pickup is then measured, and if the measurement results are a specified threshold value or higher it is determined that the optical disc being played is an inferior disk. The focus and tracking balance amounts are then adjusted to as to reduce the error rate to a minimum level.

BACKGROUND OF THE INVENTION

1. Field Of The Invention

The present invention relates to optical pickup control circuitirradiation control for controlling irradiated light irradiated to anoptical disc, for reading-in data stored on an optical disc.

2. Description Of The Related Art

Up to now, optical discs such as CDs and DVDs have spread widely, andoptical disc reproduction devices exist for reading out data stored inthese optical discs.

An optical disc is disc-shaped, and data is recorded by forming pits ofdiffering length in a spiral shape on a signal recording surface. In anoptical disc reproduction device, laser light is then irradiated to theoptical disc and data is read by detecting pits based on reflectedlight. In order to perform this reading, it is necessary to focus theirradiated light on the optical disc surface, and also to performtracking so that the irradiated light is always irradiated on the pits.

A focus servo system and a tracking servo system, for carrying outfeedback control of a focus condition and a tracking condition ofreflected light in response to the state of the reflected light aretherefore provided in an optical disc reproduction device.

In this way appropriate focus control and tracking control can beperformed, and optimum optical disc reproduction can be carried out.

However, there are situations where sufficient reproduction can not beperformed, because of variations in sensitivity of light receivingelements of the optical pickup irradiating laser light on the opticaldisk, or poor optical disc quality.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an optical pickup forappropriately controlling irradiated light irradiated to an opticaldisc, for reading data stored on the optical disc.

The present invention generates an irradiation error signal representinga degree of irradiation error for irradiated light from light intensityconditions of light reflected from an optical disc, and controlsirradiated light irradiated to the optical disc from the optical pickupin response to this irradiation error signal. In this way, irradiatedlight control can be carried out in the same way as under normalconditions. With the present invention, an error rate in read signalerror correction is then detected, and if this error rate is a specifiedthreshold or higher, irradiated light is controlled so that the errorrate is reduced. As a result, even if an optical disc is of inferiorquality this can be coped with and reading is made possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an embodiment of the presentinvention.

FIG. 2A, FIG. 2B and FIG. 2C are drawings showing the principal of focuserror detection using an astigmatism method.

FIG. 3 is a drawing showing a circuit structure for detecting andoutputting a focus error signal using an output signal from a foursegment detection sensor.

FIG. 4 is a drawing showing the circuit structure detecting andoutputting a tracking error signal using an output signal from a foursegment detection sensor.

FIG. 5A, FIG. 5B and FIG. 5C are drawings showing arrangement of a lightspot on an optical disc for tracking error detection.

FIG. 6 is a drawing showing process flow for measuring error rate andadjusting balance in response to the measured amount.

FIG. 7 is a drawing for describing an ECC (error correction code) block.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, Reference numeral 1 represents an optical disk, on which asignal is recorded as data on a signal recording surface of thedisc-shaped recording medium utilizing the fact that it is possible toform pits of differing length in a spiral shape. Reference numeral 2 isa optical pickup, having a laser light generating section forirradiating laser light to the optical disc 1, a cylindrical lens usedin an objective lens for aligning a focus point of light reflected bythe optical disc and in an astigmatism method, and a light receivingsection formed as a four segment sensor for converting a beam focused bythis lens into the signals B1-B4 shown in FIG. 2A-2C.

According to the principles of the astigmatism method, when the focalpoint is offset by the optical disc 1 approaching the objective lens, abeam has a shape as shown in FIG. 2B, and the levels of received lightsignals B2 and B4 from the four segment sensor become higher than thelevels of signal B1 and B3. Also, when the focal point is offset by theoptical disc moving away from the objective lens, the beam has a shapeas shown in FIG. 2C and the levels of received light signals B1 and B3become larger.

Reference numeral 3 is an RF amplifier, for outputting an RF signal, afocus error signal FE and a tracking error signal TE. Received lightsignals B1-B4 output from the optical pickup 2 are amplified, and thefour signals B1-B4 are added together and output as the RF signal. FIG.3 is a computation circuit for generating the focus error signal FE. Thesignals B1-B4 are operated on in the computation circuit shown in FIG. 3to calculate ((B1+B3)−(B2+B4)), and the result of that calculation isoutput as the focus error signal FE.

Further, FIG. 4 is a circuit for generating the tracking error signalTE. Signals B1-B4 are manipulated in the phase determining circuit ofFIG. 4 to calculate (B1+B3) and (B2+B4), the calculated signals aresubjected to phase comparison, and a tracking error signal TE is outputfrom the RF amplifier 3 according to the comparison results. In moredetail, as shown in FIG. 5A, when tracking slips so that the pits are atthe lower side and the beam advances from left to right in the drawing,only output signals B2 and B3 from the four segment sensor react toreceived light, and so (B1+B3) including the initially reacting signalB3 is advanced in phase compared to (B2+B4), and the tracking errorsignal TE is output as a positive level. As shown in FIG. 5E, whentracking slips so that the pits are at the upper side and the beamadvances from left to right in the drawing, only output signals B1 andB4 from the four segment sensor react to received light, and so (B2+B4)including the initially reacting signal B4 is advanced in phase comparedto (B1+B3), and the tracking error signal TE is output as a negativelevel. As shown in FIG. 5C, when tracking is aligned, if the boundary ofB1 and B4, and of B2 and B3, is position at the center of a pit signalsB3 and B4 react at the same time, and so (B1+B3) and (B2+B4) are inphase, and the tracking error signal TE becomes a zero level.

Reference numeral 4 is a servo circuit, for judging levels of the focuserror signal FE and the tracking error signal TE output from the RFamplifier 3, and outputting focus and tracking balance control signalsFBAL and TEAL for controlling focus and tracking.

Reference numeral 5 is a driver for outputting focus and trackingactuator drive signals to the optical pickup 2 in response to the focusand tracking balance signals FBAL and TEAL.

Reference numeral 6 is a signal processing circuit for EFM subjectingthe RF signal to EFM demodulation in the case of a CD, or subjecting theRF signal to EFM+(eight to sixteen modulation) demodulation in the caseof a DVD (digital Versatile Disc). The demodulated signal is thensubjected to error detection and correction by the error detection andcorrection circuit 7, and an error rate depending on the errorcorrection results is measured. Reference numeral 8 is a microcomputerfor judging the focus error signal FE, tracking error signal TE anderror rate and outputting and setting data for focus and trackingbalance amounts to the servo circuit 4.

First of all, balance amounts to make positive and negative directionsignal levels for predetermined specified focus and tracking errorsignals zero levels from outside are set in the servo circuit 4 asinitial settings when turning the power on.

In response to the initially set balance amounts for the focus andtracking error signals, focus and tracking balance signals FBAL and TBALare output from the servo circuit 4. Once this is carried out, drivesignals for the optical pickup 2 are output from the driver 5 inresponse to the focus and tracking balance signals EBAL and TBAL. Drivesignals for the optical pickup 2 in an orthogonal direction and a radialdirection with respect to the optical disc are then output from thedriver 5 in response to the focus and tracking balance signals FBAL andTBAL.

Next, at the optical pickup 2, laser light is irradiated, a beamreflected by the optical disc 1 is received by a four segment sensor ofa light receiving sections and signals B1-B4 are output from the foursegment sensor in response to the received beam. The focus error signalFE and tracking error signal TE from the RF amplifier 3 are then outputbased on the signals B1-B4. In this way, using the optical pickup 2 adata signal is read from the optical disk 1 and that read signal isoutput.

After that, the signal read by the optical pickup 2 is amplified by theREF amplifier 3, and that amplified signal, namely the RF signal, andthe focus error signal FE and the tracking error signal TE correspondingto the read signal, are output from the RF amplifier 3.

The level of the focus error signal FE is then detected by the servocircuit 4, and the focus balance signal FBAL is adjusted and output soas to make the focus error signal FE a zero level, as in FIG. 2A. Inthis way, if the focus error signal FE becomes a zero level, theadjustment and output is finished at an optimum point for the balanceamount of the focus error signal. The focus error signal FE is thuscoarsely controlled.

The level of the tracking error signal TE is then detected by the servocircuit 4, and the tracking balance signal TBAL is adjusted and outputso as to make the tracking error signal TE a zero level. The adjustmentand output is then finished with a value of the tracking balance signalto make the tracking error signal TE a zero level at the optimum pointfor tracking balance amount. The tracking error signal TE is thuscoarsely controlled.

This completes initial adjustment of focus and tracking balance amounts,and audio or visual playback is then achieved through signal processing,in the signal processing circuit, of a playback signal from the opticaldisc based on the RF signal that constitutes a data signal output fromthe RF amplifier 3 based on signals B1-B4, while maintaining the optimumpoints of the focus error signal FE and the tracking error signal TEthrough fine adjustment of the focus error signal FE and the trackingerror signal TE.

The pits can be determined according to standards, and have any one ofnine lengths, from 3 to 11, with 3 being the shortest.

It is possible to obtain optimum points for balance amounts for bothfocus and tracking through adjustment. With this embodiment, balanceamounts are adjusted further. This will be described using the flowchartof FIG. 6.

First of all, the signal processing circuit 6 demodulates the RF signal,that demodulated signal is subjected to error detection and correctionby the error detection and correction circuit 7, and the error rateresulting from the error correction is measured (S1).

Calculation of the error rate will now be described. FIG. 7 is one ECC(error correcting code) block conforming to the DVD standard.

First of all, error detection and correction is performed on the blockof the first column, using row symbol parity (PI), and a block errorrate number for the first row is calculated using an arithmeticexpression. Continuing on, the block error rate number for the secondrow is then calculated. In this way respective row data error correctionis executed according to respective row symbol parity (PI), and errorcorrection numbers are calculated corresponding to the respective rowsymbol parity (PI). Each calculated error rate is stored in a registerinside the error detection and correction circuit 7, and once errorrates have been calculated for all row blocks, the respective errorrates are finally read out from all of the registers, a sum of the rowdata error correction numbers is calculated by the error detection andcorrection circuit 7, and this is stored in a register inside aninterface to the microcomputer as an overall error rate.

Next, the microcomputer 8 designates an address of an interface registerfor the error detection and correction circuit 7, and an error rate isread out from this register and compared with a specified threshold. Ifthe error rate is equal to or greater than the specified threshold, itis then judged that the optical disk being replayed is inferior, or thatthe characteristics of the optical pickup are poor, and processingadvances (S2).

A specified tracking balance amount, being a limit range (traverselevel) that a tracking servo can follow, is set in the microcomputer 8,and this value is transferred from the microcomputer 8 to the servocircuit 4 (S3). In the servo circuit 4, a tracking loop is forcibly setmoving away from an optimum point according to this tracking balanceamount.

Error detection and correction is carried out with the tracking balanceamount set in step S3, and the error rate is measured. Error rate isthen transferred to the microcomputer 8 as an error rate relative to aspecified value of the tracking balance amount and stored in memory ofthe microcomputer 8 (S4).

After storing in memory, it is determined whether error rate has beenmeasured for a plurality of tracking balance values, and processingadvances if it is determined that measurement is complete. On the otherhand, if measurement of error rate for a plurality of tracking balanceamount values is not complete, processing returns to steps S3 and S4,and processing continues a number of times. In this way, a tracking loopis forcibly set in response to a plurality of tracking balance amounts,error rate is measured each time this is done, and the results arestored in the memory of then microcomputer 8 (S5).

If all measurement is complete, the microcomputer 8 detects the lowesterror rate from amongst the error rates stored in memory, reads out thetracking balance amount for when the error rate is lowest and sets thattracking balance amount in the servo circuit 4 as a new optimum valuefor tracking balance amount. In this way, the tracking balance amountbecomes a value that minimizes the error rate, and setting of trackingbalance amount is complete (S6).

A specified focus balance amount, being a limit range (S-characterlevel) that a focus servo can follow, is set in the microcomputer 8, andthis value is transferred from the microcomputer B to the servo circuit4 (S7). In the servo circuit 4, a focus loop is forcibly set moving awayfrom an optimum point according to this focus balance amount.

Error detection and correction is carried out with the focus balanceamount set in step S7, and the error rate is measured. Error rate isthen transferred to the microcomputer 8 as an error rate relative to aspecified value of the focus balance amount and stored in memory of themicrocomputer 8 (S8).

After storing in memory, it is determined whether error rate has beenmeasured for a plurality of focus balance values, and processingadvances if it is determined that measurement is complete. On the otherhand, if measurement of error rate for a plurality of focus balanceamount values is not complete, processing returns to steps S7 and S8,and processing continues a number of times. In this way, a focus loop isforcibly set in response to a plurality of focus balance amounts, errorrate is measured each time this is done, and the results are stored inthe memory of the microcomputer 8 (S9).

If all measurement is complete, the microcomputer 8 detects the lowesterror rate from amongst the error rates stored in memory, reads out thefocus balance amount for when the error rate is lowest, makes that focusbalance amount a new optimum focus balance amount and sets that focusbalance amount in the servo circuit 4. In this way, the focus balanceamount becomes a value where the error rate becomes minimum, and settingof focus balance amount is complete

In this way, setting of focus and tracking amounts with the lowest errorrates is carried out, and it is possible to perform optical diskplayback with improved playability.

On the other hand, when the detected error rate is less than thespecified threshold value in step S2, it is determined that playback issatisfactory with conventional tracking and focus balance amountsetting, processing terminates without adjustment of focus and trackingbalance amounts originally set in the servo circuit 4 and playbackbegins.

In this manner, focus and tracking are carried out so that the focuserror signal FE and the tracking error signal TE having conventionalservo adjustment become substantially a zero level, further errordetection and correction is carried out by the error detection andcorrection circuit 7, the measured error rate is judged throughcomparison with a predetermined specified threshold value, balanceamounts are changed a number of times within a range of focus balanceamount and tracking balance amount the servo can follow, and error ratesare measured for the respectively changed balance amounts. Balanceamounts for when the measured error rate is less than the specifiedthreshold, and when error rate is minimum, are set in the servo 4, andoptical disk playback is carried out.

With the embodiment of the invention, initially tracking balance amountis varied, error rate is measured and tracking balance amount isoptimally adjusted, but it is also possible to carry out optimaladjustment of focus balance amount first.

Also with the embodiment, error rate is measured and both tracking andfocus balance are adjusted, but it is also possible to only adjust oneof either focus balance or tracking balance.

Further, with the embodiment, tracking and focus balance amount arevaried a specified number of times and error rate is measured, but it isalso possible, if a changed balance amount has an error rate less than aspecified threshold value, to make the balance amount at that time theoptimum amount and advance to the next processing step.

The specified threshold for error rate is a value predetermined based onan error rate obtained by playing back a plurality of optical discswhere pit accuracy reaches a level defined in the optical disc standard,and inferior optical discs that do not reach that level.

In the description above, by simply carrying out automatic adjustment toadjust focus and tracking balance amounts for only original focus andtracking error signals, it is possible to prevent situations where thereis reduction in playability due to inferior optical discs or variationin optical pickup characteristics to an extent that playback can not beperformed, and where there is a lot of block noise in the reproducedimage even when playback is possible, and playability can therefore beimproved.

According to the present invention, if an error rate determined by theerror correction circuit is greater than a specified threshold afteradjustment of focus and tracking balance amounts, it is determined thatan optical disk is of poor quality, and focus and tracking balanceamounts are readjusted so that the error rate becomes a minimum valueand the optical disk is played back. It is therefore possible toreliably improve playability of inferior discs.

It is also possible to bring about improvement in playability of opticaldiscs without additional new circuitry, because error rate output froman error correction circuit is measured and focus and tracking balanceamounts are determined to optimum points.

1-9. (canceled)
 10. An optical pickup control circuit for controllingirradiated light irradiated to an optical disc, for read data recordedon the optical disc, comprising: an irradiation error signal generatingcircuit for generating an irradiation error signal representing a degreeof irradiation error for irradiated light from a light amount conditionof light reflected from the optical disc; a servo circuit for generatingbalance signals for controlling irradiated light irradiated to theoptical disc from the optical pickup in response to the irradiationerror signal; an error correction circuit for carrying out errorcorrection for a read signal obtained based on the light reflected fromthe optical disk and detecting an error rate for error correction; asignal processing circuit for demodulating the read signal to obtain ademodulate signal; and a servo control circuit for changing balancesignals used by the servo circuit on the basis of the error rate of thedemodulate signal so that the error rate is made smaller, in the eventthat the error rate detected in the error correction circuit is aspecified threshold value or higher; wherein the error correctioncircuit carries out error correction for the demodulate signal after thedemodulate signal is obtained by the signal processing circuit; andwherein the irradiation error signal is a signal representing a degreeof irradiated light focus error, and the balance signals are signals forcontrolling focus of the optical pickup.
 11. The optical pickup controlcircuit of claim 10, wherein: the servo control circuit sequentiallychanges balance signals, error rates detected at that time by the errorcorrection circuit are compared, and a balance signal giving a minimumerror rate is used.
 12. The optical pickup control circuit of claim 11,wherein: the servo circuit changes the balance signals within a rangethat can be followed by the irradiation control for the optical pickup.13. The optical pickup control circuit of claim 10, wherein: the servocontrol circuit sequentially changes balance signals, and a balancesignal of the balance signals, having a error rate detected at that timeby the error correction circuit that is less than the threshold value,is used.
 14. The optical pickup control circuit of claim 13, wherein:the servo circuit changes the balance signals within a range that can befollowed by the irradiation control for the optical pickup.
 15. Anoptical pickup control circuit for controlling irradiated lightirradiated to an optical disc, for read data recorded on the opticaldisc, comprising: an irradiation error signal generating circuit forgenerating an irradiation error signal representing a degree ofirradiation error for irradiated light from a light amount condition oflight reflected from the optical disc; a servo circuit for generatingbalance signals for controlling irradiated light irradiated to theoptical disc from the optical pickup in response to the irradiationerror signal; an error correction circuit for carrying out errorcorrection for a read signal obtained based on the light reflected fromthe optical disk and detecting an error rate for error correction; asignal processing circuit for demodulating the read signal to obtain ademodulate signal; and a servo control circuit for changing balancesignals used by the servo circuit on the basis of the error rate of thedemodulate signal so that the error rate is made smaller, in the eventthat the error rate detected in the error correction circuit is aspecified threshold value or higher; wherein the error correctioncircuit carries out error correction for the demodulate signal after thedemodulate signal is obtained by the signal processing circuit; andwherein the irradiation error signal is a signal representing a degreeof irradiated light tracking error, and the balance signals are signalsfor controlling tracking of the optical pickup.
 16. The optical pickupcontrol circuit of claim 10, wherein: the irradiation error signalincludes both a signal representing degree of irradiated light focuserror and a signal representing degree of irradiated light trackingerror; and the balance signals include both a signal for controllingfocus of the optical pickup and a signal for controlling tracking of theoptical pickup.
 17. The optical pickup control circuit of claim 16,wherein: the servo control circuit first sequentially changes balancesignals of either one of focus or tracking, compares error rates foreither focus or tracking detected at that time by the error correctioncircuit, and determines a balance signal for either focus or trackinggiving a minimum error rate, and subsequently, sequentially changesbalance signals of the other one of focus or tracking, compares errorrates for the other one of focus or tracking detected at that time bythe error correction circuit, and determines a balance signal for theother of focus or tracking giving a minimum error rated.
 18. The opticalpickup control circuit of claim 15, wherein: the servo control circuitsequentially changes balance signals, error rates detected at that timeby the error correction circuit are compared, and a balance signalgiving a minimum error rate is used.
 19. The optical pickup controlcircuit of claim 18, wherein: the servo circuit changes the balancesignals within a range that can be followed by the irradiation controlfor the optical pickup.
 20. The optical pickup control circuit of claim15, wherein: the servo control circuit sequentially changes balancesignals, and a balance signal of the balance signals, having a errorrate detected at that time by the error correction circuit that is lessthan the threshold value, is used.
 21. The optical pickup controlcircuit of claim 20, wherein: the servo circuit changes the balancesignals within a range that can be followed by the irradiation controlfor the optical pickup.
 22. The optical pickup control circuit of claim15, wherein: the irradiation error signal includes both a signalrepresenting degree of irradiated light focus error and a signalrepresenting degree of irradiated light tracking error; and the balancesignals include both a signal for controlling focus of the opticalpickup and a signal for controlling tracking of the optical pickup. 23.The optical pickup control circuit of claim 22, wherein: the servocontrol circuit first sequentially changes balance signals of either oneof focus or tracking, compares error rates for either focus or trackingdetected at that time by the error correction circuit, and determines abalance signal for either focus or tracking giving a minimum error rate,and subsequently, sequentially changes balance signals of the other oneof focus or tracking, compares error rates for the other one of focus ortracking detected at that time by the error correction circuit, anddetermines a balance signal for the other of focus or tracking giving aminimum error rated.